问题补充:
7.Although the causes of cancer , we do not yet have any practical way to prevent it.
A. are being uncovered
B. have been uncovering
C. are uncovering
D. have uncovered
答案:
(答案→)A. are being uncovered
B. have been uncovering
C. are uncovering
D. have uncovered
解析:分析语境逻辑不难发现,该空表示“现在正在被揭示”,应填现在进行时被动语态动词形式are being uncovered。